Rectification of gaseous mixtures



I N VEN TOR. Ala man Jena/ cf HTTURNEY Filed June 18, 1949 M BENEDICT RECTIFICATION OF GASEOUS MIXTURES W 5% 3w hw Feb. 10, 1953 a wwww Maw N atented Pet). 10,

UNITED STATES PATENT o'FF 'icE 2,627,731 treatments as GASEOUS MIX ems Mattresses;named, 36: Hydrocarbon Research, Inc.',New York','N;Y.','"a" corporation'of New Jersey Application June 1-8, 1949,--saa1 No. asst scram. (01. 62 17515) This invention relates to the production of oxygen by the liquefaction and rectification of air under relatively low pressures, i. e'., pressures not substantially above that required to overcome friction losses in the flow of, the gas strearns through the equipment iii which the process is carried out. p e

All temperatures herein are in degrees; F. pres,- sures in pounds per square inch gauge and per centages by volume, unless otherwise specified;

Among the objects of this invention is'to provide a low pressure process of producing oxygen by the liquefaction andrectification of air which involves a material reduction in the power consumption required for its practice. v

Another object is to provide such process which can be carried out in rectification equipmentof smaller volumetric capacity with consequent sav ing in the cost of the rectification equipment.

Other objects and advantages of this invention will be apparent from the following detailed description thereof. 7 v

In accordance with this inventiong thef air is compressed to a pressure" notf substantially in excessof that required toovercomefric'tion losses involved in the'fiow of the air and the rectification products through the'equipment'. Theco'rfnpressed air after cooling byheat exchangewith one or more rectification products is introduced: mm a e ca on ieie i which' uid refl x at the bottom of thejrectificationi sys'teniand at an intermediate level of the] rectification system: is subjected to refbojilingandthe resultahtvapors' passed upwardly through the system, The' top gaseous rectification product; i. e.', nitrogen, sses from the top ofthe rectification system through a heat exchange zone wherein it is warmed by in direct heat exchange with the incoming air stream and/ or a recyelestream' of the top gaseous rectification product which is subsequently used to effect the aforesaid re-boi'ling ofliq'uid' reflux in the rectification system. Part of the warmed top product is withdrawn as top product and an other part forms the rec'yclestrearn. Therec'ycle' stream is compressed; cooled torernove the heat of compression, and divided into ttvo'portion's. One portion of the] compressed recycle stream is cooled by indirect'heat exchange with a rectification product stream and then utilized to re -boil" liquefied while eifecting the: re-looiling of the liquid reflux of therectification' system and both;

partially liquefied portions are-passed "through wil i d usa' ii rt lis'fili r led. Bo h rr; ti d and, g cl o t ns. rt ea stream are" discharged into theto'p' of the rec-T ifica i n s tem to S ly li uid fi xther h jrfli i e l i i'fe l itth p.

fi" ct strea wnich, as the. ten of ,the atexgchanfejz'one e as. top pjrqdua and ti'fi'caticnsystern as the y, 3 QrI more ies'an'd/or paral- A a t o h a 1's me ia. fiQL i 'e is eib ilsh; Fo .7 pril s rationaud n '1' t e inte sii ofwsimpli i yj [exchan er i shcwnyasfcomprising woparalllel' wpaths. Ac-f lle lm, ow re x aeli ie in B h e c a r. ay; cqmpr e" JLml I iD t3? @Qf" f fiOW ieit si hfle. the ft fh schees r ef' jdoe i a invention and as' it'may pe of" type it is believed further d'e use th'ercr t en" th ii'i 'pl eh' in orede Air linejwilead nto' n no al sealin th exit'"efid"of "pat in indire t in the upper section of the rectification system C. Desirably, the rectification system C comprises two sections and H each provided, as customary, with rectification plates of the bubble cap or other desired type. Both sections l0 and H are operated at a pressure which differs from the inlet pressure by the pressure drop which takes place in the flow of the air through the system. In general the pressure will not exceed about 6 pounds per square inch.

A line 22 leads from the top of column section H1 and is provided with branches 23, 24, branch 23 leads to flow path l3 for supplying this path with a stream of nitrogen product flowing therethrough in indirect heat exchange relation with the air flowing through path |2. The nitrogen warmed in its flow through path l3 leaves this path through an exit line 25, Branch 24 communicates with path M of exchanger B. A liquid nitrogen reflux line 25 leads into the top of section Ill.

The base of section H1 is provided with a line 21 through which reflux liquid is withdrawn. Line 21 passes through a heat exchanger 28 and communicates with branches 29 and 30. Branch 29 leads into the base of section l0. Line 27, heat exchanger 28 and branch 29 constitute reboiler R communicating with the base of section l0. Branch 30 is provided with a valve 3| for controlling flow therethrough and leads into the top of section II, desirably of somewhat smaller volumetric capacity than section l9.

Section N is provided with a line 32 for the flow of vapor from the top of this section into the base of the upper section H). The base of section H is provided with a line 33 for the flow of reflux liquid through an exchanger 34. Line 33 communicates with a return line which leads into the base of section H. Line 33, exchanger 34 and return line 35 constitute re-boiler Ft communicating with the base of section Oxygen line 36 leads from the base of section II into path N5 of exchanger B. An exit line 37 leads from the exit end of this path.

From path H a line 38 leads into the nitrogen exit line 25. Communicating with line 25 is a line 39 which leads into a compressor 40 of any well known type. From the compressor the compressed gas flows through a cooler 4| and thence into a line 42 provided with two branches 43 and 44. Branch 44 communicates with a second compressor 45 and branch 43 with the flow path I5 of the exchanger B. The exit end of this flow path is provided with a line 46 which leads into the heat exchanger 28. A line 41 provided with an expansion valve 48 therein connects exchanger 28 with the liquid nitrogen reflux line 49 at 50.

From the compressor 45 the gas further compressed therein, flows through a cooler 5| thence through line 52 into the flow path I! of exchanger B. This flow path is provided with an exit line 53 provided with branches 54 and 55, the latter branch leadsinto the heat exchanger 34. A line 56 provided with an expansion valve 51 connects exchanger 34 with the reflux line 49 at 58. Line 49 communicates with the reflux line 26 leading into the top of section Ill.

Branch 54 leads into a refrigerating system 59 of any well known type for supplyingv a refrigerating medium, such as boiling methane, for cooling the nitrogen passing through the refrigerating system. The system operates to cause the flow of the refrigerating medium in indirect heat exchange relation with the nitrogen, the rates of flow and temperatures of these media bein controlled so that enough cold is introduced by refrigeration, at this point in the process, to compensate for most if not all of the cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectification and for heat leaks into the system. A line 60 provided with an expansion and flow controlling valve 5| connects the refrigerating system 59 with the reflux line 26.

In operation, air compressed to a pressure of from 2 to 10 pounds per square inch is passed through flow path l2 in indirect heat exchange relation with a stream of nitrogen flowing from the top of section it! through line 22, branch 23 and flow path 3. The thus cooled air flows through line l9 and enters section iii where it is rectified, producing crude oxygen and the nitrogen product of rectification. In the rectification system nitrogen vapors containing some oxygen rise through the column countercurrent to the descending liquid nitrogen reflux introduced through line 26, the nitrogen reflux liquid being thus vaporized and the reflux liquid becoming progressively richer in oxygen flowing downwardly through the column. The reflux liquid from the base of section H3 passes through line 27 of re-boiler R and is thus partially vaporized. The vapor liquid mixture thus produced flows in part through line 29 into section id. The remaining liquid flows through line 39 into section H where it provides the reflux liquid for this section. The division of liquid between the two streams flowing through lines 29 and 3B is controlled by valve 3|.

A stream of nitrogen is continuously withdrawn through branch 24, flows through flow path M in indirect heat exchange relation with the compressed nitrogen stream flowing through flow path 15. The nitrogen flowing through I4 is thus warmed, exits through line 33 and mixes with the nitrogen flowing through line 25. Of the resultant mixed nitrogen a portion is withdrawn as product through line 32 and the remainder passed through line 39 to compressor 40. lhe nitrogen is compressed in this compressor to a pressure of from 35 to 55 pounds per square inch, the heat of compression removed in cooler 4| and then divided into two streams in its flow from line 42 into the two branches 43 and 44. One stream consisting of approximately from one-fourth to one-third of the nitrogen thus compressed passes through line 43, path |5, into and through line 43 and exchanger 28 where it effects re-boiling of the reflux liquid flowing through this exchanger. {he mixture or" vapors and liquid thus produced flows in part through line 29 into section It providing the vapor rising through this section and in part into the top of section providing the reflux for this section. The nitrogen flowing through exchanger 23 is condensed and the resultant condensate passed through expansion valve 48 whereby the pressure thereon is reduced to a pressure substantially the same as, or slightly above that in the top of section lit.

The remainder of the nitrogen consisting of approximately from three-fourths to two-thirds of the nitrogen compressed in compressor .23 flows through branch 34 and enters a second compressor 45 where it is further compressed to a still higher pressure of the order of 60 to pounds. From this compressor, the nitrogen flows through cooler 5| and line 52 int-o and through path I? in indirect heat exchange relation with the oxygen flowing through path I6.

The nitrogen is thus cooled and the cool nitrogen passed through line 53.

A portion of the nitrogen from line 53 is passed through line 54, refrigerating system 59, line 89, valve 61 and into and through line 26. The amount of nitrogen thus passed through line 54 is controlled by the setting of valve Bl. Upon flow through valve 6 I, the pressure of the nitrogen is reduced to a pressure substantially the same as or slightly above that in the top of section Hi. In its flow through the refrigerating system 59 refrigeration is imparted to the nitrogen stream suificien-t to compensate for most if not all of the enthalpy losses and heat leaks into the system. Further refrigeration is imparted to the nitrogen stream upon its expansion in its now through valve 6|.-

The remainder of the nitrogen from line 53 flows through line 55 into and through exchanger 34, where it eifects re-boiling of the reflux oxygen liquid flowing from section H. The oxygen vapors thus produced flow through line 39 to provide the vapor loading forcolumn section ll. Oxygen is passed through line 35, flow path 1 6 in exchanger B and is withdrawn as product through line 31.

The nitrogen flowing through exchanger 34 is condensed and upon flow of the condensate through expansion valve '51 the pressure thereon is reduced. Both streams of nitrogen condensate thus producedflow into and through line 49 into the line 26 where they mix with the nitrogen flowing through line 25 from line 69. The resultant nitrogen mixture enters the top of section 19 where it serves as reflux liquid.

fincondensed vapors leave the top of section H through line 32 and enterthe base of section ill where they flow countercurrent to descending reflux liquid passing through this section.

The modification of Figure 2 differs from that of Figure 1 chiefly in the following respects:

(1) The rectification system consists of a unitary column instead of the two distinct sections of Figure 1;

(2) The re-boilers are built into the column and are not separate units as in Figure 1;

(3) The exchanger system involves five flow paths and not six as in Figure l; and

(4) Mostif not all of'the refrigeration re quired to compensate for enthalpy losses and heat leaks into the system is provided by expanding a portion of the compressed nitrogen and not by imparting refrigeration thereto from an extraneous source as in Figure l.

In Figure 2', the exchanger has five fiowpaths 6 5, 69, 61, 6B and 69 each provided with fins of high heat conducting material as in the case of the How paths of exchangers'AandB of Figure 1.

Air line 10 leads into the i'i'owpath 69. Line H leads from the exit end of path 65 to an intermediate point 12 in the upper portion of the rectification system C. Desirably, the rectification system C comprises a unitary column con sisting of an upper portion 13 and a lower portion 14, each providedwith rectification plates of the bubble cap or other desired type. Upper portion 13 is closed at its base by a plate 15 forming at the base of portion l3- a receptacle for crude liquid oxygen which. is subjected to reboiling. A passageway 76 extends through this plate 15 and connects the top of the lower portion with the base of the upper portion 13. As in the modification of Figure 1, the rectification column C'- is operated at a pressure which differs from the air inlet pressure by the pressure 6 drop which takes place through the system.

A line 11 leads from the top of the column C and is provided with two branches 18 and 19. Branch 18 leads into flow path 66. Branch 19 passes into a heat exchanger which is provided with a line 8| leading therefrom into the flow path 66, entering this flow path at a point somewhat above the point where line 18 enters thereintoi In this way the nitrogen warmed in its flow through exchanger 89 enters flow path 86 at a point therein where the temperature issubstantially the same as that of the nitrogen flowing through line 8|. Nitrogen thus introduced into path 66 flows.therethrough, is warmed and leaves this path through an exit line 82 Communicating with line 82"is a line 83 which leads into a compressor 84 of any well known time From this compressor compressed gas flows through cooler 85 and thence into a line provided with two branches 86 and 81. Branch 86 communicates with a compressor 88 and in the flow of the air branch 81 withthe flow path 61. The exit end of this flow path is provided with aline 89 which communicates with a coil 99 immersed in the body of crude liquid oxygen maintained at the base of the upper portion 13 of the rectification column C. A line 9| provided withan expansion valve 92 leads from this coil99 into a liquid ni trogen reflux line 93. Thecoil 99 immersed in the body of crude liquid oxygen corresponds to the re-boiler R of Figure 1.-

From compressor 88, the nitrogen further compressed therein 'fiows through a cooler and thence through line 95 into the flow path 69. From the exit end of this flow path a line 95 leads into a coil 91 immersed in the body of liquid oxygen maintained at the base of the lower portion 14 of the rectification system C. A line 98 extends from coil 91 through exchanger 89 and is provided with an expansion valve 99. This line communicates with the liquid nitrogen. reflux line 93 leading-into the top of the rectifi cation column (3' The coil 9'! immersed in the body of liquid oxygen corresponds to re-'-'- boiler B A second line I leads from near the base of flow path 69 into an expander H which may be an expansion engine or turbine of any conven v tional type. Line I02 leads from this expander and communicates with the line 18 entering flow path 66. The nitrogen passing through expander-l9! is expanded producing most if not all ofthe refrigerationnecessary to compensate for enthalpy losses and heat leaks into the system. Some refrigeration is also produced upon expansion of the nitrogenstre'ams flowing through theexpansion valves 92 .and 99.

An oxygen line I03 leads from near the base of column portion 14 to the flow path 88i An oxygen product exit line I94 leads from the top of this flow path.

One example-of the operation of the process of this invention in the apparatus shown in Fig use 2 of the drawing is described below. It will be understood this example isvgiven for'purposes of exemplification only and theinvention is not limited thereto. The example refersto an o'xy-- gen plant operating in a locality where the atmospheric pressure is 14.7 pounds per square inch absolute.

Air which has been treated to remove therefrom condensible impurities, such as moisture andcarbon dioxide, is'compressed to a pressure of about 6:pounds and at a'temperature of 77 F.

introduced into flow path 65. The air is introduced at the rate of M4 tons per hour. It flows therethrough in indirect heat exchange relation with the nitrogen flowing through path 66. The air is thus cooled to a temperature of 309.4 F. and at this temperature and a pressure of 4 pounds enters the rectification column C at 12. Nitrogen rectification product at a temperature of 3l8 F. and a pressure of 3 pounds is withdrawn from the top of column C through line 11. 25.5% of this nitrogen flows through line 19, exchanger 80 where its temperature is raised to 294.9 F., then through line 8| entering the flow path 66 at a point where the temperature therein is approximately 294..9 F.

The remainder of the nitrogen (74.5%) from the top of the rectification column mixes with the nitrogen from the expander Ill! which is also at a temperature of -318 F. and a pressure of 3 pounds and flows through line 13 into flow path 5%. Nitrogen is withdrawn through line 82 at approximately atmospheric pressure and a temperature of 72 F. About 108.5 tons per hour of nitrogen consisting of approximately 99% by volume of nitrogen is withdrawn as product through line K15.

The remainder of the nitrogen is passed through line 83 into the compressor 8% where the nitrogen is compressed to a pressure of about 37 pounds. The nitrogen flows; through cooler at where the heat of compression is removed and at a temperature of 77 F. and a pressure of 37 pounds flows in part through line 81 into the flow path 61 and the remainder flows through line 86 to the compressor 88. Approximately 124.5 tons per hour of nitrogen is recycled. Of the recycled nitrogen approximately 25% is passed through line 81 into the flow path 87 and the remaining-75% introduced into the second compressor 88.

The nitrogen leaves flow path 61 at a temperature of 298.2 F. and a pressure of 35 pounds, flows through coil 90 where it is condensed and efiects vaporization of the crude liquid oxygen providing part of the vapor rising through portion 13 of column C. From the coil 90 the condensed nitrogen at a pressure of 34 pounds flows through line 9|, is flashed in its flow through valve 92 to a temperature of 318.2 F. and a pressure of 3 pounds at which temperature and pressure it enters the reflux line 93 leading into the top of the rectification system.

In the compressor 88 the nitrogen is compressed to a pressure of about 62 pounds. This compressed nitrogen flows through cooler 94, where the heat of compression is removed, and thence through line 95 into flow path 69 entering this flow path at a temperature of 77 F. and a pressure of 62 pounds. Of the nitrogen flowing through flow path 69, about 65% flows through line 9t. Th'm portion of the nitrogen at a temperature of --289.9" F. and a pressure of 60 pounds flows through coil 9'! at the base of the portion 14 of the rectification column effecting vaporization of the liquid oxygen in which the coil is immersed, the vapors rising through the lower portion M of the column countercurrent to the descending reflux liquid provided by the overflow of the crude liquid oxygen maintained at the base of upper portion 73 which overflow passes through the passageway 16 into the top of portion 74.

The nitrogen in its flow through coil 97 is condensed. The liquid nitrogen thus produced at a temperature of 289.9 F. and a pressure of 59 pounds flows through line 98 and exchanger 80 in indirect heat exchange relation with the gaseous nitrogen flowing through line 19 into this exchanger. From exchanger 88 the nitrogen at a temperature or" -303 F. and a pressure of 58 pounds flows through the expansion valve 99 where it is flashed to a temperature of 318.2 F. and a pressure of 3 pounds. At this temperature and pressure it mixes with the nitrogen entering line 93 from line 9! and the resultant mixed nitrogen stream consisting of a mixture of liquid and gaseous nitrogen flow into the top of the rectification column C providing the reflux for the vapors rising through this column.

Approximately 32.5 tons per hour of nitrogen is withdrawn through line Hill at a. temperature of 257.5 F. and a pressure of 61 pounds and introduced into the expander Hll. This corresponds to 35% of the total nitrogen introduced into the flow path E9 or 26% of the total nitrogen recycled. The nitrogen leaving the expander at a temperature of 318 F. and a pressure of 3 pounds mixes with that entering line 18 from line I? and the resultant mixed nitrogen stream enters the inlet end of flow path 66 as hereinabove described.

Oxygen is withdrawn through line its from the base of portion M of the column at a temperature of 294.9 F. and is introduced into the flow path 68 where it flows in indirect heat exchange relation with the high pressure nitrogen. The oxygen product is withdrawn through line 594 at a temperature of 72 F. and a pressure of 2 pounds. Oxygen of purity is withdrawn at a rate of 35.5 tons per hour.

The work required to eflect compression of the nitrogen passed through the re-boilers 99 and 91' providing the necessary vapor loading of the rectification system in the above example producing oxygen of 90% purity is 8,260 horsepower. For purposes of comparison it is noted that operating under substantially the same conditions but eflecting vaporization of the reflux only at the base of the fractionating column, as is conventional practice, 8,710 horsepower is required. Thus, this invention results in a saving of 5% of the work required to effect compression of the nitrogen in carrying out the process.

Best engineering practice dictates compressing the nitrogen in three stages to raise it to the pressure of approximately 62 pounds at which it is passed through the body of liquid oxygen maintained at the base of portion 14 of the column to eifect re-boiling. The amount of work required to effect such compression of the nitrogen in the third stage of the present invention is 1,350 horsepower. Operating in accordance with heretofore conventional technique involving re-boiling the liquid reflux entirely at the base of the column and compressing the nitrogen in three stages 1,790 horsepower is required to effect the compression in the third stage. 01 the work required to effect the third stage of compression, this invention, it will be noted, effects a saving of 24.5%.

The above saving is substantially greater when producing an oxygen product of higher purity. For example, for an oxygen of 98% purity the over-all saving in energy instead of 5%. is approximately 7%, and the saving in energy required for the third stage of compression is correspondingly greater than the 24.5% value above given.

It has been found that the high pressure nitrogen stream passed through re-boiler R or coil 91 effects efiicient re-boiling of the reflux liquid to provide the necessary vapor loading for section i l and portion 74, respectively. The medium pressure nitrogen stream flowing through reboiler R or coil 93 likewise efiects efiicient reboiling of the reflux liquid to provide the necessary vapor loading for section It! and portion i3, respectively. The latter reflux liquid is at a lower temperature and hence can be re-boiled or vaporized by the nitrogen stream at a lower pressure with simultaneous condensation of this nitrogen stream. In this way a material saving in the power consumption is effected since, in accordance with the present invention, the nitrogen employed to efiect re-boiling of the refiux liquid is not all compressed to the high pressure required in effecting re-boiling in re-boiler R. or coil 9? but a substantial portion, about one-fourth or even more of the nitrogen is compressed to a lower pressure and employed at this lower pressure to effect the desired re-boiling. Further by employing at least two re-boilers associated with separate zones of the rectification system, the lower zone may be made of materially smaller capacity than would otherwise be the case with consequent saving in the construction costs for the rectification equipment.

Since certain changes may be made in carrying out the above process without departing from the scope of this invention it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense. Thus, for example, while the invention ha been described in connection with the production of oxygen by the liquefaction and rectification of air, it will be understood it is not limited thereto but includes the treatment of mix tures of other gases to effect their separation, for example the rectification of natural gas having an appreciable nitrogen content. While two reboilers have been shown, it will be understood a greater number may be used spaced along the height of the fractionating column to give optimum results. When using two re-boilers in an oxygen process, the re-boiler at the intermediate level is preferably disposed at a point where the vapor in the column contains about 50% to 60% nitrogen. The other re-boiler is of course located at or near the base of the rectification column.

The term reflux liquid is used in the claims, to mean the liquid in the rectification column including the liquid which collects therein at the bottom of the column; thus referring, for example, to Figure 1, this term includes not only the liquid introduced through line 26 into the top of section ill but, also the liquid which collects at the base of this section.

What is claimed is:

1. A process of rectifying a gaseous mixture to recover two gaseous rectification products, each in substantial proportion, which comprises rectifying said gaseous mixture in a rectification zone through which a liquefied portion of said gaseous mixture descends from the upper end to the lower end of said zone, subjecting said liquefied portion to reboiling when passing through a region of said zone intermediate said upper and lower ends and again to reboiling when reaching said lower end, recovering a top gaseous rectification product in substantial proportion from said upper end and a bottom gaseous rectification product in substantial proportion from said lower end, compressing part of said top product, dividing the compressed part into two streams, passing one of said streams in indirect heat exchange relation with the liquefied portion passing through the intermediate region of said zone to effect said reboiling, further compressing the other of said streams, passing the further compressed stream in indirect heat exchange relation with the liquefied portion reaching said lower end to effect again said reboiling, thereafter decompressing said two streams and discharging them into said upper end of said zone.

2. A process of rectifying air to recover gaseous oxygen and nitrogen rectification products, each in substantial proportion, which comprises rectifying air in a rectification zone through which a liquefied portion of said air descends from the upper end to the lower end of said zone, subjecting said liquefied portion to rebelling when passing through a region of said zone intermediate said upper and lower ends and again to reboiling when reaching said lower end, recovering gaseous nitrogen rectification product in substantial proportion from said upper end and gaseous oxygen rectification product in substantial proportion from said lower end, compressing part of said nitrogen product, dividing the compressed part into two streams, passing one of said streams in indirect heat exchange relation with the liquefied portion passing through the intermediate region of said zone to effect said reboiling, further compressing the other of said streams, passing the further compressed stream in indirect heat exchange relation with the liquefied portion reaching said lower end to effect again said reboiling, thereafter decompressing said two streams and discharging them into said upper end of said zone.

3. The process of claim 2 wherein the rectification zone is maintained at a gauge pressure of from 2 to 10 pounds per square inch, the compressed part of said nitrogen product is at a gauge pressure of from 35 to 55 pounds per square inch, and the further compressed stream is at a gauge pressure of from 60 to pounds per square inch.

4. The process of claim 1 wherein a portion of the further compressed stream is withdrawn therefrom prior to the passage of said further compressed stream in indirect heat exchange relation with the liquefied portion, and the portion thus withdrawn is expanded with the performance of external work to produce refrigeration.

5. The process of claim 2 wherein a portion of the further compressed stream is withdrawn therefrom prior to the passage of said further compressed stream in indirect heat exchange relation with the liquefied portion, and the por-- tion thus withdrawn is expanded with the periormance of external work to produce refrigera- MANSON BENEDICT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,040,112 Van Nuys May 12, 1936 2,095,809 Gomonet Oct. 12, 1937 2,180,435 Schlitt Nov. 21, 1939 OTHER REFERENCES Blast Furnace and Steel Plant for October 1948, pp. 1212-1215. 

